babel-jest-assertions

0.1.0 verified Mon Apr 27 auth: no javascript

A Babel plugin (v0.1.0) that automatically inserts `expect.assertions(n)` and `expect.hasAssertions()` into Jest test blocks by counting `expect` calls. It supports sync, async, arrow, named, and only tests, including `beforeEach`/`afterEach` blocks. Unlike manual insertion, it eliminates human error and verbosity. Current stable version is 0.1.0; no major releases planned. Minimal alternative to manual assertion count management.

Common errors

error TypeError: babel is not a function ↓

cause Using plugin with Babel 7+ without updating Babel API

fix

Downgrade to Babel 6 or use the Babel 7 compatible fork of this plugin.

error ReferenceError: expect is not defined ↓

cause Plugin inserts `expect.assertions` but `expect` is not in scope (e.g., missing `@jest/globals` import in ESM).

fix

Add import { expect } from '@jest/globals'; to test files or configure Jest globals properly.

error The plugin "babel-jest-assertions" didn't return a function. ↓

cause Using plugin string in Babel config but plugin module not installed.

fix

Run npm install --save-dev babel-jest-assertions and ensure it's in node_modules.

Warnings

gotcha Plugin counts `expect` calls, not actual assertions; non-standard matcher chains may be miscounted. ↓

fix Manually add `expect.assertions(n)` if the count is off, or avoid complex expect chains.

gotcha Does not support dynamically computed assertion counts; `expect.assertions` uses a static integer. ↓

fix Use manual `expect.assertions(0)` or disable plugin for dynamic cases.

breaking In v0.1.0, support for counting `expect` in `beforeEach` and `afterEach` was added; existing tests may fail if those blocks contain assertions they didn't before. ↓

fix Review tests that have assertions in lifecycle hooks; adjust expected counts or add assertions.

gotcha Plugin may not work with custom test wrapper functions (e.g., `describe.each`) if they don't match internal patterns. ↓

fix Ensure test blocks use standard `it`, `test`, `xit`, `fit`, `it.only` only.

Install

npm install babel-jest-assertions

yarn add babel-jest-assertions

pnpm add babel-jest-assertions

Imports

(plugin)

wrong

import babelJestAssertions from 'babel-jest-assertions'

correct

Add `'babel-jest-assertions'` to your `.babelrc` plugins array

This is a Babel plugin, not a runtime module. Use in Babel configuration only.

Quickstart

Shows Babel plugin configuration and how the plugin transforms a test with two assertions.

// .babelrc
{
  "plugins": ["babel-jest-assertions"]
}

// test.js
it('counts assertions', () => {
  expect(1 + 0).toBe(1);
  expect(0 + 1).toBe(1);
});
// Transforms to:
// it('counts assertions', () => {
//   expect.hasAssertions();
//   expect.assertions(2);
//   expect(1 + 0).toBe(1);
//   expect(0 + 1).toBe(1);
// });